The present invention relates to determining the transmit location of an unknown emitter.
Existing techniques for determining the location of an unknown emitter which is being transmitted across satellites in the geostationary/geosynchronous orbit require at least two satellites. Generally speaking, these geolocation techniques work as follows. Two satellites, called the primary and the adjacent satellite, receive the signal transmitted from the unknown emitter. The two satellites relay the transmitted signal to a ground receiving station. The ground station computes the time difference of arrival (TDOA) and the frequency difference of arrival (FDOA) between the two signals relayed by the satellites. The location of the unknown emitter is obtained using the TDOA, the FDOA and the satellite ephemeris data. If only either the TDOA or the FDOA is observed, an additional adjacent satellite is necessary to provide an additional TDOA or FDOA measurement for localization. A reference emitter whose transmit position is known can be used to reduce the amount of uncertainty in satellite positions and velocities to improve the localization accuracy. However, if only one satellite is available, neither TDOA nor FDOA can be measured for geolocation.